Larger tumbler barrel questions

[andyiii]

Hey folks,

I've just started my first stage 1 run in a Rebel 17 tumbler and have a few questions that I have not found answers to yet:

1)  this is a 17 lb. barrel and it rotates at exactly 20 rpm.  Is that too slow?  I feel like I've seen folks talking about tumbling at 40 rpm.  I realize that slower = gentler, but it has to be fast enough to be effective; need that happy medium.

2)  I used 16 tablespoons of 60/90 SiC to get things going.  I just learned that 16 tablespoons = 1 cup.  That seemed like an excessive amount of grit as I poured it in.  With larger barrels do you still use roughly 1 tbsp per pound of rock?

3)  Just as with the 3 lb. barrels, I used only rocks (various sizes) for stage 1, no media.  Is this correct or do I need cushioning media since the rocks are falling further as they turn?

4)  Since this barrel is so much bigger and the rocks are also, should I consider starting with a grit coarser than 60/90 SiC?

Thanks,
Andy III

[pebblesky]

1. I remembered seeing discussion about low-speed Rebel 17 here. 20 rpm should do fine.
2. I think I use a bit over one cup. Seems to work fine. No noticeable unused grit left after a week of tumbling.
3. I don't use media for Rebel 17 either. I use small agate fillers, which is more for carrying the grits around and grinding effectively, than serving as cushioning.

[saaz]

Can't comment on 1.
2. I use 3/4 cup in a 12lb Lortone, so that seems about right. My grit seems to be all used up at the end of a week.
3. For stage 1 in the 12lb I use only rocks (unless I have new ceramic that I want to smooth off). I also try to add some small rocks as filler.
4. I wouldn't worry about it. I recently posted about an experiment where I found 120/220 was equally as effective as 60/90 in my 12lb, if measured by weight. Someone else tested a 3lb and found 120 was *more* effective iirc. That all started with an old article that found 80 to 220 was the ideal range.

[andyiii]

Great info! Thanks, all!